Gear assembly

ABSTRACT

A gear assembly for high-speed transmission between either two parallel shafts or two intersecting shafts comprising two meshing gears, one mounted to a drive shaft and the other mounted to a driven shaft, each of the gears having coaxially disposed first and second toothed portions which differ from each other in that the teeth of the first toothed portion are cut at a first inclination angle and the teeth of the second toothed portion are cut at a second inclination angle different from the first inclination angle. One of the meshing gears is fixed to its shaft so as to be non-displaceable axially, while the other is mounted so as to be axially displaceable with respect to the fixed gear. Preloading means engaging the movable gear are provided for applying an axially directed load to the movable floating gear thereby urging the floating gear against the fixed gear so as to eliminate the free angular displacement of the gears with respect to each other within backlash and to preclude tooth disengagement under axial forces which are imposed on the floating gear by external peripheral loads.

BACKGROUND OF THE INVENTION

The present invention relates to gearing for high-speed transmissionand, more particularly, to high-speed gears having two toothed portionsjuxtadisposed on a shaft for use in applications wherein the absorptionof dynamic loads, the elimination of backlash and the minimizing ofnoise and vibration are critical.

In certain high-speed applications, for example in turbomachinery, gearsmay be subjected to high dynamic loads. Unavoidable inaccuracies in theteeth mesh due to tolerance, as well as errors in manufacturing andassembly, lead to high-frequency periodical accelerations of the drivengear which result in the imposition of acceleration forces on themeshing teeth. Due to the presence of backlash between non-working teethflanks, the acceleration of the driven gear leads also to separation ofthe working teeth followed by a reengagement thereof resulting in animpact load being imposed on the gear teeth. This phenomenon, known asfree impact or hammering, results in high dynamic loading on the gearteeth with attendant noise generation and vibrations occurring.Additionally, in symmetrical double helical or herringbone type gears,the teeth meshing errors cause the uneven distribution of applied loadbetween the two toothed portions of the gear. Accordingly, efforts havebeen made when designing double toothed helical gears to eliminate or atleast to reduce these disadvantages.

For example, in U.S. Pat. No. 2,982,146 there is disclosed a gearmechanism wherein one gear is axially fixed while the other gear is freemove axially along its shaft or axially together with its shaft. Eachgear is comprised of two assymmetric toothed portions with the teeth onone toothed portion having a helix angle of less than 45° pitched in onedirection while the teeth on the other toothed portion has a helix angleof more than 45° pitched in the opposite direction. The free floatinggear serves to distribute a transmitted load between the two toothedportions of the gear in inverse proportion to the relationship betweenthe tangents of the two helix angles, the load on both toothed portionsof each gear being applied in the same direction. Because thesubstantially greater part of applied load is taken-up permanently bythe toothed portion having the lesser helix angle, this gearing is lesssensitive to the variations of load-distribution due to mesh errors thanis gearing of the symmetrical herringbone type. However, this gearing isstill subject to hammering due to the absence of backlash take-upcapability.

An example of anti-backlash gearing is presented in U.S. Pat. No.3,648,534. As disclosed therein, one of the meshing gears is split gearhaving two toothed portions which are not integral but rather areangularly adjustable. One of the toothed portions of the split gear isfixed to the shaft while the other to free to rotate about the shaftunder the influence of a biasing means which controls the angulardisplacement between the two portions of the split gear. The biasingmeans imposes an additional load on the gear teeth which permanentlyacts on the teeth and can lead to undue wear and gear loadingsparticularly in high speed applications.

U.S. Pat. No. 4,036,074 discloses anti-backlash gearing of the splitgear type wherein the split gear has two toothed portions whose teethhave the same helix angle and pitch direction. One portion is fixed tothe shaft while the other portion is axially movable along the shaft andseparated therefrom by spring biasing means. The spring means serve tourge the movable toothed portion of the split gear away from the fixedtoothed portion of the split gear. The maximum displacement of themovable portion away from the fixed portion is preadjusted to apreselected distance to limit backlash. Although, this gear arrangementsubject to reduced backlash, backlash still exists and, in fact,actually varies from one pair of engaging teeth to the next pair ofengaging teeth.

It is the primary object of the present invention to provide a gearassembly having meshing gears of the double toothed portion type whereinthe free impact (hammering) of teeth is eliminated without imposingadditional loading on the teeth.

SUMMARY OF THE INVENTION

A gear assembly for high-speed transmission between either two parallelshafts or two intersecting shafts comprising two meshing gears, onemounted to a drive shaft and the other mounted to a driven shaft, eachof the gears having coaxially disposed first and second toothed portionswhich differ from each other in that the teeth of the first toothedportion are cut at a first inclination angle and the teeth of the secondtoothed portion are cut at a second inclination angle different from thefirst inclination angle. One of the meshing gears is fixed to its shaftso as to be non-displaceable axially, while the other is mounted so asto be axially displaceable with respect to the fixed gear. Preloadingmeans engaging the movable gear are provided for applying an axiallydirected load to the movable floating gear thereby urging the floatinggear against the fixed gear so as to eliminate the free angulardisplacement of the gears with respect to each other within backlash andto preclude tooth disengagement under axial forces which are imposed onthe floating gear by external peripheral loads.

Due to the urging by the preloading means of the floating gear againstthe fixed gear, the teeth of the first toothed portion of the floatinggear intermesh with the teeth of the first toothed portion of the fixedgear and the teeth of the second toothed portion of the floating gearintermesh with the teeth of the second toothed portions of the fixedgear along the opposite tooth flanks with respect to each other.

As the teeth of the first toothed portions of the gears are cut at adifferent inclination angle than the teeth of the second toothedportions of the gears, the loading on the gears is distributed with thetoothed portion having the lesser inclination angle taking-up theoverall transmitted load and with the toothed portion having the greaterinclination angle serving to prevent free angular displacement of thegears with respect to each other within backlash thereby eliminatingteeth hammering. The peripheral forces which arise due to the tendencyof the teeth to separate subsequent to acceleration of the driven gearare taken-up by the toothed portion having the greater inclination anglein a direction opposite to the transmitted load.

The first and second inclination angles at which the teeth are cut inthe first and second toothed portions of each gear are selected inrelationship to the peripheral forces applied to the first and secondtoothed portions so that the axial preloading thrust is sufficient tobalance and oppose the reaction forces imposed on the floating gear andmaintain engagement of the gear teeth, but not so excessive as to causeunnecessary tooth wear due to overpressure during tooth engagement. Whenhigh damping and compactness are desired, the greater inclination angleis set at a value of 90° and the lesser inclination angle preselected ata value in range from at least 45° to less than 90°.

Additionally, it is preferred that the toothed portion of at least oneof the meshing gear portions having the greater inclination angle ismanufactured with a vibration and noise damping or dissipating materialsuch as powdered metal or plastics.

Further, at least one of the gears is preferably comprised of first andsecond toothed portions which are angularly displaceble with respect toother whereby the first and second toothed portions of the gear may beselectively positioned about the shaft with respect to each other so asto provide mutual compensation of the cyclical variations of gear ratiowhich unavoidably occur due to variations in teeth in the manufacturingprocess.

Also, the number of teeth cut into the first toothed portion and thenumber of teeth cut into the second toothed portion of each gear areselected to be at different numbers such that the ratio of the number ofteeth cut in the two portions is not an integer. Also, the number ofteeth cut in the first portion of the floating gear and in the secondportion of the floating gear are respectively related to the number ofteeth cut in the first portion of the fixed gear and in the secondportion of the fixed gear such that the gear ratio between the firsttoothed portions of the gears and the gear ratio between the secondtoothed portions of the gears are at the same whole number value.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described in the followingdiscussion of the preferred embodiments thereof with reference to theaccompanying drawing, wherein:

FIG. 1 is an elevational view, partly in section, showing a gear housingincorporating the inventive concept hereof for the high-speedtransmission between parallel shafts;

FIG. 2 is an alternate embodiment of the meshing gear grouping of FIG.1;

FIG. 3 is a diagrammatic illustration of the engagement of the teeth ofthe gear assembly of FIG. 1 wherein the teeth of the two toothedportions of each gear have the opposite pitch;

FIG. 4 is a diagrammatic illustration of the engagement of the teeth ofthe gear assembly of FIG. 1 wherein the teeth of the two toothedportions of each gear have the same pitch;

FIG. 5 is a diagrammatic illustration of the engagement of the teeth ofthe gear grouping of FIG. 2;

FIG. 6 is an elevational view, partly in section, showing a gear housingincorporating the inventive concept hereof for the high-speedtransmission between intersecting shafts;

FIG. 7 is an alternate embodiment of the meshing gear grouping of FIG.6;

FIG. 8 is a diagrammatic illustration of the engagement of the teeth ofthe gear assembly of FIG. 6 wherein the teeth of the two toothedportions spiral in opposite directions;

FIG. 9 is a diagrammatic illustration of the engagement of the teeth ofthe gear assembly of FIG. 6 wherein the teeth of the two toothedportions of each gear spiral in the same direction; and

FIG. 10 is a diagrammatic illustration of the engagement of the teeth ofthe gear grouping of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is depicted therein a gear assembly 1 forthe high-speed transmission between two parallel shafts 3 and 5, one ofwhich is a drive shaft and the other of which is a driven shaft. Thegear assembly 1 comprises first and second meshing gears 2 and 4enclosed within housing 6 and mounted respectively to the shafts 3 and 5with the first gear 2 being mounted so as to be axially movable alongthe shaft 3 and with the second gear 4 being fixedly mounted to theshaft 5 by means well known in the art. Shafts 3 and 5 are eachrotatably supported along parallel axes by bearings 7 and 8 and 14 and15, respectively, mounted in the housing 6 and secured therein by endcaps 16 bolted to the housing 6. Bearings 7 and 15 are combined axialand radial thrust type bearings chosen to be capable of withstandingaxial load, while bearings 8 and 14 need only be pure radial thrust typebearings.

The gears 2 and 4 are disposed along their respective shafts 3 and 5such that their teeth intermesh. Preloading means 10 is disposed on theshaft 3 between the axial and radial thrust bearing 7 and the floatinggear 2 to provide an axial preloading thrust against the floating gear 2so as to urge the floating gear 2 towards the fixed gear 4 mounted toshaft 5. The preloading means 10 comprises a resilient element 11, suchas a spring-type cup washer or elastic pads, and adjustments meanscomprising tension nut 12 and lock nut 13. By rotating the tension nut12 and lock nut 13 the compression on the resilient element 11 may bechanged thereby adjusting the preloading thrust on the floating gear 2.

Each of the gears 2 and 4 are formed of coaxially disposed first andsecond assymetric toothed portions 22 and 24 and 42 and 44 respectively.The gears may be formed of two asymmetrically toothed portions cut onseparate blanks as illustrated in FIG. 1, or they may be formed of twoasymmetric toothed portions cut on a single blank. With the first andsecond toothed portions 42 and 44 being cut on separate blanks, thetoothed portion 42 and 44 may be angularly displaceable with respect toeach other. As shown in FIG. 1, the second toothed portion 44 of gear 4is rotatable about the shaft 5 to be selectively angularily displaceablewith respect to the first toothed portion 42 of gear 4. Once positionedangularily with respect to the first toothed portion 42, the secondtoothed portion 44 is locked into position by attachment to the firsttoothed portion 42 of gear 4.

By the term "asymmetric", it is meant that the first and second toothedportions of each of the gears have teeth cut therein having differenthelix angles. That is, the helical angle of the teeth 32 of the firsttoothed portion 22 of the floating gear 2 is different from the helixangle of teeth 34 of the second toothed portion 24 of the floating gear2. Similarly, the helix angle of the teeth 52 of the first toothedportion 42 of the fixed gear 4 is different from the helix angle ofteeth 54 of the second toothed portion 44 of the fixed gear 4. The teeth32 and 34 and the teeth 52 and 54 although having different helix anglesmay be of the same direction in pitch or of the opposite direction inpitch as illustrated in FIG. 1.

Additionally, the helix angles of the teeth 32 and 34, and the teeth 52and 54, are selected such that the ratio of the tangent of the helixangle of the teeth 32, 52 respectively on the first toothed portions 22and 42 to the tangent of the helix angle of the teeth 34, 54respectively on the second toothed portions 24 and 44 is substantiallyequal to the ratio of the magnitude of the peripheral forces on thesecond toothed portion to the magnitude of the peripheral forces on thefirst toothed portion.

In FIG. 2, the helix angle of the teeth 32 on the first portion 22 ofthe floating gear 2 is selected to be at least 45° and less than 90°while the helix angle of the teeth 34 on the second portion 24 of thefloating gear 2 is selected to be equal to 90°. Similarly, the helixangle of the teeth 52 on the first portion 42 of the fixed gear 4 isselected to be at least 45° and less than 90° while the helix angle ofthe teeth 54 on the second portion 44 of the fixed gear 4 is selected tobe equal to 90°. In this range of values for the helix angle, thefriction between intermeshing teeth provide a damping capability.

The engagement of the teeth in the gear assembly of the invention isdiagrammatically illustrated in FIGS. 3 and 4 for the gear asemblyembodied in FIG. 1 with the teeth of the two tooth portions of each gearbeing pitched in opposite directions in FIG. 3 and being pitched in thesame direction in FIG. 4. The engagement of the teeth of the gearing ofFIG. 2 is similarily illustrated in FIG. 5.

In the FIGS. 3, 4 and 5, the arrow 21 indicates the direction of therotation of the floating gear 2, the arrow 23 indicates the direction ofthe axial preloading thrust applied to the floating gear 2, β1represents the lesser pitch helix angle, which is associated with theteeth 32 and 52 of the first toothed portions of each of the gears, andβ2 represents the greater helix angle, which is associated with theteeth 34 and 54 of the second toothed portions of each of the gears.

Referring now to FIG. 3, the axial preloading force 23 urges thefloating gear 2 against the fixed gear 4 so that tooth 32 engages thetooth 52 of the fixed gear with the flank which is opposite to the flankof tooth 34 which engages the tooth 54 of the gear 4 whereby freeangular displacement of the gears within backlash is prevented and thepossibility of hammering is eliminated. The axial reactions generated bythe engagement of the teeth 32, 34 of the floating gear 2 with the teeth52, 54 of the fixed gear 4 at their contacting surface is opposed andbalanced by the axial preloading thrust 23. Due to the opposite pitch ofthe teeth on the two toothed portions of each gear, these engagementreactions act in the same direction and alternatively oppose the axialpreloading thrust 23 which is accordingly selected to counter balancethe larger of these engagement reactions and thereby prevent teethseparation at the working surfaces and ensure no contact between theunworking surfaces of the teeth. The permanent separation of non-workingteeth flanks reduces the generation of noise due to the discharge of airand oil trapped in the mesh.

If an external force, such as transmitted load, is applied to the tooth32 of the first portion against the direction of rotation indicated bythe arrow 21, the axial thrust on tooth 32 is increased so as toautomatically unload the engagement of teeth 34 and 54. Similarly, if anexternal force is applied to the tooth 34 of the second toothed portionin the direction of the rotation, the axial thrust on tooth 34 will leadto unloading the engagement of teeth 32 and 52.

In order to prevent tooth separation under external loading, the axialpreload must be selected to be equal to or greater than the maximumaxial component of the external peripheral loads applied to the teeth.In order to prevent overloading of the teeth by an axial preload, theratio of the tangent of the greater helix angle β2 to the tangent of thelesser helix angle β1 is chosen to be substantially equal to the ratioof the peripheral load on the tooth 32 on the first portion of the gearto the peripheral load on the teeth 34 on the second portion of thegear. The peripheral loads on the first and second portions of the gearare determined analytically and/or emphirically to calculate the ratioupon which the helix angles β1 and β2 will be selected. The axialpreloading thrust can be adjusted once the gear assembly is in operationto compensate for any inaccuracy in determining the peripheral loadsupon which the ratio is calculated.

In the embodiment shown in FIG. 4 wherein the teeth of the first andsecond toothed portions of the gear have the same pitch direction, theapplication of an external force to the tooth 32 of the first portion ofthe gear against the direction of rotation will result in a wedging ofrather than an unloading and separation of teeth 34 and 54, while theapplication of an external force to the tooth 34 of the second portionof the gear in the direction of the rotation will again result in anunloading and separation of the teeth 32 and 52. Therefore, the axialpreloading force which should be applied to prevent separation need onlybe equal to the maximum component of the external peripheral loadapplied to tooth 34.

The difference in helical angles, β2-β1, should be large enough to avoida jamming of the teeth 32, 34 by the teeth 52, 54 due to excessivefrictional forces on the teeth during engagement. Accordingly, thedifference in helix angles, β2-⊕1, must be greater than the equivalentangle whose tangent is the sum of the coefficients of friction betweenboth sets of meshing teeth and also the coefficient of friction of thefloating gear 2 along its shaft.

In the embodiment shown in FIG. 5 wherein the helix angle β2 of theteeth of the second toothed portion equals 90° and the helix angle β1 ofthe teeth of the first toothed portion is less than 90°, both sets ofengaging teeth 32, 52 and 34, 54 are involved in load transmission fromthe gear 2 to the gear 4. The thrust 23 meshes the teeth 34 of thesecond portion of the gear 2 with the teeth 54 of the second portion ofthe gear 4. A peripheral load applied to tooth 32 on the first portionof gear 2 against the direction of rotation will also cause an axialforce meshing the teeth 34 of the floating gear with the teeth 54 of thefixed gear. This axial force will exceed the corresponding peripheralload because of the large magnitude of the helix angle β1. Together withthe thrust 23, this axial force provides a friction engagement of theteeth 34 and 54 which will transmit a portion of the external load. Thefriction engagement of the teeth 34 with the teeth 54 caused by thethrust 23 also serves to resist the unmeshing of the teeth 32 and 52subsequent to acceleration of the driven gear and thereby provide adamping action on the gearing.

Additionally, if the magnitude of helix angle β1 is selected in thepreferred range of from at least 45° to less than 90°, a smooth andquiet operation of the first toothed portions can be attained with areduced number of teeth thereby enabling a compact gear assemblyconstruction with a large gear ratio.

The difference in helix angles β2-β1 should be selected to be largeenough to avoid the jamming of the teeth 32, 34 by the teeth 52, 54,respectively, due to excessive frictional forces on the teeth duringengagement. Accordingly, the difference 90-β1 should be greater than theequivalent angle whose tangent is equal to the sum of the coefficientsof friction between tooth sets of the meshing gears.

Referring now to FIG. 6, there is depicted therein a gear assembly 71for the high-speed transmission between two intersecting shafts 73 and75, one of which is a drive shaft and the other of which is a drivenshaft. The gear assembly 71 comprises first and second meshing gears 72and 74 enclosed within housing 76 and mounted respectively to the shafts73 and 75 with the first gear 72 being mounted so as to be axiallymovable along the shaft 73 and with the second gear 74 being fixedlymounted to the shaft 75. Shafts 73 and 75 are each rotatably supportedon intersecting axes by bearings 77 and 78 and 84 and 85, respectively,mounted in the housing 76 and secured therein by end caps 86 bolted tohousing 76. Bearings 77 and 85 are combined axial and radial thrust typebearings chosen to be capable of withstanding axial load, while bearings78 and 84 need only be pure radial thrust type bearings.

The gears 72 and 74 are disposed along their respective shafts 73 and 75such that their teeth intermesh. Preloading means 80, comprising aresilient spring-type cup washer 81 and tension nut 82 and lock nut 83,is disposed on the shaft 73 so as to urge the floating gear 72 towardsthe fixed gear 74 mounted to the shaft 75.

The first gear 72 is comprised of first and second toothed bevelportions 92 and 94 which are connected together to be rotatablydisplaceable with respect to each other and are axially displaceablealong the shaft 73. Both the first and second toothed bevel portions 92and 94 have the same pitch cone but the teeth cut in the first toothedbevel portion 92 are cut at a different spiral angle than the teeth cutin the second toothed bevel portion 94. Additionally, the bevel portions92 and 94 may have a different number of teeth.

The second gear 74 also comprises first and second toothed portions 96and 98 which are mounted coaxially on the shaft 74 and are angularilydisplaceable with respect to each other. The first and second toothedportions 96 and 98 are again asymmetric in that the teeth cut in thefirst portion 96 are cut at a different angle than the teeth cut in thesecond portion 98.

An alternate embodiment of gear grouping 71 of FIG. 6 is shown in FIG.7. As depicted therein, the first toothed portion 92 of the first gear72 and the first toothed portion 96 of the second gear 74 have spiralteeth cut therein, while the second toothed portion 94 of the first gear72 and the second toothed portion 98 of the second gear 74 have teethcut at an angle of inclination of 90° to their respective shafts.

The engagement of the teeth in the gear assemblies of the presentinvention is diagrammatically illustrated in FIGS. 8 and 9 for the geargrouping shown in FIG. 6 and in FIG. 10 for the gear grouping embodimentshown in FIG. 7. In the engagement shown in FIG. 8, the lesser spiralangle is on the toothed portions 92 and 96 and the teeth on the firstand second toothed portions are cut in opposite directions. In FIG. 9the lesser spiral angle is on the toothed portion 98 of the fixed gearand the teeth on both toothed portions thereof are cut in the samedirection, while the floating gear has a uniform tooth partern. In FIG.10, the angle β2 is 90°.

In FIGS. 8, 9 and 10, the arrow 100 indicates the direction of therotation of the floating gear 72, and the arrow 101 indicates thedirection of the axial preloading thrust applied to the floating bevelgear 72, β1 represents the spiral angle at the contact point of theteeth 91 cut in the first toothed bevel portion 92 of the first gear 72and also the teeth 95 cut in the first toothed portion 96 of the secondgear 74, and β2 represents the spiral angle at the contact point of theteeth 93 cut in the second toothed bevel portion 94 of the first gear 72and also the teeth 97 cut in the second toothed portion 98 of the secondgear 74.

The operation of the gear assemblies of FIGS. 6 and 7 as illustrated inFIGS. 8, 9 and 10 is similar to the previously described operation ofthe gear assemblies of FIGS. 1 and 2 as illustrated in FIGS. 3, 4 and 5.The reactions generated by the application of peripheral loads duringthe engagement of the gear teeth as shown in FIG. 8 is balanced andopposed by the axial preloading thrust in a manner similar to thatdescribed previously with respect to the engagement of the teeth of thegear assembly for transmission between parallel shafts as illustrated inFIG. 3. Likewise, the reactions generated by the application ofperipheral loads during the engagement of the gear teeth as shown inFIG. 9 is balanced and opposed by the axial preloading thrust in amanner similar to that described previously with respect to theengagement of the teeth of the gear assembly for transmission betweenparallel shafts as illustrated in FIG. 4. Similarly, the reactionsgenerated by the application of peripheral loads during the engagementof the gear teeth as shown in FIG. 10 is balanced and opposed in amanner similar to that described previously with respect to theengagement of the teeth of the gear assembly for transmission betweenparallel shafts as illustrated in FIG. 5.

In the tooth engagement illustrated in FIG. 9, both tooth formations arecut in the same direction and one of the gears is formed on a singleblank rather than of two distinct portions as the other gear. Thisspecific embodiment, which results in a cost savings, is made possiblewithout departing from the invention by cutting the teeth 91 in the gearwith a continuously varying spiral angle. The first and second portionsof the second gear are angularily displaceable with respect to eachother and are adjusted such that the teeth 95 and 97 of the first andsecond portions thereof, respectively, engage the tooth 91 of the firstgear on opposite sides thereof and at points of differing spiral anglealong tooth 91. The teeth engagement obtained in this manner results inreactions balanced and opposed by the axial preloading thrust asdescribed with respect to FIG. 4.

As described previously with respect to transmission between parallelshafts, it is necessary to preselect the values for β2 with respect toβ1 based on expected peripheral loads in order to effectively providefor the balancing of these peripheral loads by the axial preloadingthrust but prevent tooth overloading. In the case of transmissionbetween intersecting shafts, i.e. for the gear assembly of FIG. 6wherein the gears have oppositely pitched toothed portions, the angle β2and the axial preloading force are selected based not only onanalytically and/or emphirically determined values for peripheral loads,but also on the pitch angle of the floated bevel gear and the toothpressure angle through the following relationships: ##EQU1## and

    A=KW.sub.1 cos γ

where:

A is the axial preloading force;

W₁, W₂ are the total peripheral forces applied to the first and to thesecond toothed portions respectively;

φ is the normal tooth pressure angle; is the pitch angle of the bevelgear;

C equals (tan φ)·(tan γ); and

K equals (tan β1)±(C/cos β1).

The sign of the term (C/cos β1) in the expression for K depends on thedirection of the gear's rotation and the pitch direction. For theembodiment shown in FIG. 8, the sign is minus. From these relationships,the spiral angle β2 and the axial preloading force can be determined inorder to balance and oppose the external peripheral forces.

The spiral angle β1 is chosen in accordance with standard procedures forconventional bevel gearing. For a typical value of β1 of 30°, and for W₁/W₂ =3, φ=20° and γ=30°, the value of β2 calculated via the aboveexpression would be approximately 53.5°.

Further in accordance with the present invention, the gear assemblies ofFIG. 1 for transmission between parallel shafts and the gear assembliesof FIG. 6 for transmission between intersecting shafts can be providedwith additional noise reduction capability by proper selection of thenumber of teeth on the first and second toothed portions, by propermaterial selection in the manufacturing, and/or by proper angularpositioning of the first and second toothed portions with respect toeach other.

Accordingly, the number of teeth on the first toothed portion of eachgear and the number of teeth on the second toothed portion are selectedso as to be non-multiple with respect to each other. That is, the ratioof the number of teeth on the first portion of the gear to the number ofteeth on the second portion of the gear is a non-integer. Additionally,the number of teeth on the first and second portions of the mating gearsare chosen so that the interengaging portions have the same whole numbergear ratio.

Further, vibration and noise damping or dissipating materials, such aspowdered metals and various plastic materials, may be used inmanufacturing the gear assemblies. In accordance with the presentinvention, the toothed portion of the gears having the greaterinclination angle (i.e., the greater helical or spiral angle) is formedof or at least coated with a vibration/noise damping or dissipatingmaterial while the toothed portion of the gear having the lesserinclination angle, i.e. the portion of the gear carrying the greaterload, is made of standard, conentional load carrying material. Forexample, in the embodiment of the gear assembly shown in FIG. 1, atleast one of the toothed portions 24 and 44 would be constructed of avibration/noise damping or dissipating material. Similarly, in theembodiment of the gear assembly shown in FIG. 6, at least one of thetoothed portions 92 and 96, having the greater spiral angle, would beconstructed of a vibration/noise damping or dissipating material.

In accordance with the present invention, at least one of the meshinggears of the gear assembly of the present invention, whether for use intransmission between parallel shafts or intersecting shafts, is made offirst and second toothed portions which are angularly displaceable withrespect to each other. By proper rotation of one toothed portion withrespect to the other, the angular relationship between the teeth of thefirst and second toothed portions can be adjusted to mutually compensatefor cyclic teeth variations and periodic gear ratio variations therebylessening vibration and noise. For example, in the gear assembly of FIG.1 for transmission between parallel shafts, the second toothed portion44 of the gear 4 is rotatable about its shaft to be angularly adjustablewith respect to the first toothed portion 42 thereof. To adjust theangular position thereof, the second toothed portion 44 is unbolted fromthe first toothed portion 42, then rotated about the shaft 5 to thedesired angular position with respect to the first toothed portion 42,and then rebolted to the first toothed portion 42 to fix the new angularpositioning therebetween.

I claim:
 1. A gear assembly for transmission between a drive shaft and adriven shaft comprising:a. two meshing gears, one mounted to said driveshaft and one to said driven shaft, each of said gears having coaxiallydisposed first and second toothed portions, the teeth of the firsttoothed portion of each of said gears being at a first inclination angleand the teeth of the second toothed portion of each of said gears beingat a second inclination angle, said first and second inclination angleshaving the same pitch direction and having different values, the firsttoothed portions of said gears having interengaging teeth and the secondtoothed portions of said gears having interengaging teeth therebyestablishing a mating relationship between said gears whereby a drivingrelationship is established between said shafts, one of said gears beingaxially displaceable with respect to the other of said gears; and b.preloading means engaging said displaceable gear for applying an axiallydirected load to said displaceable gear to urge said displaceable gearagainst said other gear.
 2. A gear assembly as recited in claim 1wherein one of the first or second toothed portions of at least one ofsaid gears is non-rotatably mounted to its shaft, and the other of thefirst or second toothed portions of said gear is rotatable about itsshaft and detachably affixed to the non-rotatable portion whereby thefirst and second toothed portions of said gear are selectively angularlydisplaceable with respect to each other.
 3. A gear assembly as recitedin claim 1 wherein the number of teeth cut into the first toothedportion of each of said gears and the number of teeth cut into thesecond toothed portion of each of said gears are non-integral multiplesof each other, the ratio of the number of teeth cut into the firsttoothed portion of said movable gear to the number of teeth cut into thefirst toothed portion of said fixed gear being equal to the ratio of thenumber of teeth cut into the second toothed portion of said movable gearto the number of teeth cut into the second toothed portion of said fixedgear.
 4. A gear assembly as recited in claim 1 wherein at least onetoothed portion of said gears having the greater inclination angle iscomprised of a vibration and noise damping material and the toothedportion of each of said gears having the lesser inclination angle iscomprised of a load carrying material.